1. Technical Field
The present disclosure relates to computer motherboards, and more particularly to a computer motherboard with adjustable display data channel (DDC) in accordance with type of monitor connected to the computer motherboard.
2. Description of Related Art
A DDC is configured for a computer motherboard to access a memory of a monitor, such as an electrically erasable programmable read-only memory (EEPROM), to read extended display identification data (EDID). The EDID includes manufacturer name and serial number, product type, phosphor or filter type, timings supported by the display, display size, luminance data and (for digital displays only) pixel mapping data. A display controller may be integrated in a north bridge chip or a central processing unit, and commonly includes a first DDC for reading analog EDID and a second DDC for reading digital EDID. The display controller is connected to the monitor through a connector of the computer motherboard, such as a digital visual interface integrated (DVI-I) connector.
The DVI-I connector includes a DDC clock pin and a DDC data pin for transferring EDID. The DVI-I connector also includes a hot plug detect pin to detect whether there is a digital monitor connected to the computer motherboard through the DVI-I connector. When a digital monitor is connected to the computer motherboard through the DVI-I connector, voltage at the hot plug detect pin is higher than 0.6 volts (V). When an analog monitor is connected to the computer motherboard through the DVI-I connector, voltage at the hot plug detect pin is lower than 0.2 V.
Because the DVI-I connector includes only one DDC, and the display controller includes two DDCs for accessing digital and analog monitors, respectively. Once the computer motherboard is produced, the DDC clock and DDC data pins of the DVI-I connector are connected to corresponding pins of one of the DDCs of the display controller, so the computer motherboard is only able to access a digital monitor or an analog monitor.